Revert "Refine examples."

This reverts commit 146129279c.

examples/serde.rs

@@ -1,6 +1,19 @@
-#![cfg(feature = "serde")]
-#![cfg(not(feature = "no_object"))]
+#[cfg(any(not(feature = "serde"), feature = "no_object"))]
+fn main() {
+    println!("This example requires the 'serde' feature to run.");
+    println!("Try: cargo run --features serde --example serde");
+}
 
+#[cfg(feature = "serde")]
+#[cfg(not(feature = "no_object"))]
+fn main() {
+    example::ser();
+    println!();
+    example::de();
+}
+
+#[cfg(feature = "serde")]
+#[cfg(not(feature = "no_object"))]
 mod example {
     use rhai::serde::{from_dynamic, to_dynamic};
     use rhai::{Dynamic, Engine, Map};
@@ -75,9 +88,3 @@ mod example {
         println!("Deserialized to struct: {:#?}", x);
     }
 }
-
-fn main() {
-    example::ser();
-    println!();
-    example::de();
-}